In a cell of a cellular telecommunications system, irrespective of the particular kind of system, e.g. GSM, WCDMA, TD-SCDMA, LTE etc, there is usually a controlling station for the cell, i.e. a station which has as one of its functions to control the traffic to and from the users in the cell. A controlling station is usually equipped with an antenna arrangement which comprises a number of antennas, each of which covers one or more cells.
In each cell, regardless of the presence or absence of users in the cell, the controlling station transmits on one or more so called control channel, in order to provide control information to users in the cell. Payload traffic to the users in the cell is transmitted on so called traffic channels. This principle, i.e. control channels and traffic channels, is used in most types of cellular systems, regardless of the type of system, although the actual names of the channels may differ between e.g. GSM, WCDMA, TD-SCDMA, LTE etc.
Since transmissions on the control channel are made in a cell regardless of the presence of users in the cell, these transmissions may sometimes be a waste of energy, if there are no users in the cell. Since conservation of energy is a major concern for operators of cellular systems, this can be a problem.